CVE-2024-50694

Executive Summary

CVE-2024-50694 is a critical stack-based buffer overflow vulnerability in SunGrow WiNet-SV200 devices, specifically in firmware version WiNet-SV200.001.00.P027 and earlier. The flaw resides in the MQTT message handling routine, where the timestamp field is copied into a fixed-size stack buffer without proper bounds checking. This allows an attacker to overflow the buffer, potentially leading to remote code execution (RCE) or denial of service (DoS). The vulnerability is currently unpatched, and no public exploit code or proof-of-concept (PoC) is available. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains high due to the nature of the vulnerability and the criticality of the affected devices (solar inverters).

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded IoT device (Sungrow WiNet-SV200). No supply chain package security implications are present.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, but this is likely a placeholder. Based on the vulnerability description, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – MQTT messages are received over the network.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed to send MQTT messages.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerability affects only the device.
• Confidentiality (C): High (H) – Potential for arbitrary code execution.
• Integrity (I): High (H) – Code execution can modify device state.
• Availability (A): High (H) – Buffer overflow can cause crash or DoS.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Estimated Base Score: 9.8 (Critical)

Threat Level: Critical – Remote, unauthenticated exploitation possible with high impact.

Deep Dive & Mechanics

The vulnerability exists in the MQTT client implementation of the SunGrow WiNet-SV200 firmware. The device subscribes to MQTT topics to receive commands and data, including timestamps. When processing an incoming MQTT message, the code extracts the timestamp field and copies it into a stack-allocated buffer without verifying that the source data length does not exceed the buffer size.

Root Cause:
The function responsible for copying the timestamp uses a standard C library function like strcpy() or sprintf() without bounds checking. The stack buffer is likely of fixed size (e.g., 32 or 64 bytes), but an attacker can send a crafted MQTT message with an overly long timestamp string, causing a stack buffer overflow.

Impact:

• Stack Corruption: Overwrites return addresses, saved frame pointers, and local variables.
• Code Execution: An attacker can inject shellcode or ROP chains to execute arbitrary code with the privileges of the MQTT process (likely root).
• Denial of Service: Even without precise exploitation, the overflow can crash the device.

Attack Vector:
An attacker needs network access to the device's MQTT broker (typically on port 1883 or 8883 for TLS). The device may be exposed to the internet or accessible from the local network. The attacker publishes a malicious MQTT message to a topic the device subscribes to, containing an oversized timestamp.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern and the expected fix.

Vulnerable Code (C pseudocode):

void process_mqtt_message(char *payload) {
    char timestamp[32];  // Fixed-size stack buffer
    char *ts_start = extract_timestamp(payload);
    strcpy(timestamp, ts_start);  // No bounds check
    // ... use timestamp
}

Patched Code (Expected fix):

void process_mqtt_message(char *payload) {
    char timestamp[32];  // Fixed-size stack buffer
    char *ts_start = extract_timestamp(payload);
    strncpy(timestamp, ts_start, sizeof(timestamp) - 1);  // Bounds check
    timestamp[sizeof(timestamp) - 1] = '\0';  // Null-terminate
    // ... use timestamp
}

The fix involves replacing strcpy with strncpy or using snprintf to limit the copy length to the buffer size minus one for the null terminator.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable SunGrow WiNet-SV200 device (firmware <= WiNet-SV200.001.00.P027).
• Network access to the device's MQTT broker (default port 1883).
• MQTT client tools (e.g., mosquitto_pub).

Exploitation Steps:

1. Identify the MQTT topic: The device subscribes to a specific topic (e.g., sungrow/command). This can be discovered via network traffic analysis or device documentation.
2. Craft a malicious payload: Create an MQTT message with an oversized timestamp field. For example:

   {"timestamp": "AAAA...AAAA"}  // 100+ 'A' characters
   

3. Publish the message:

   mosquitto_pub -h <device_ip> -t "sungrow/command" -m '{"timestamp": "AAAA...AAAA"}'
   

4. Observe crash or code execution: The device may reboot, become unresponsive, or execute injected shellcode.

Note: No public exploit code is available. The above is a conceptual approach.

Blue Team (Defensive)

Detection:

• Monitor MQTT traffic for unusually long timestamp fields.
• Use network intrusion detection systems (NIDS) to flag oversized MQTT payloads.
• Implement anomaly detection on device logs for unexpected crashes or reboots.

Mitigation:

• Isolate the device on a separate VLAN with strict firewall rules.
• Disable MQTT if not required.
• Apply vendor patches when available.
• Use MQTT over TLS with client certificates to restrict unauthorized publishing.

Indicators of Compromise (IOCs)

• Network IOCs:

  • MQTT messages with timestamp fields exceeding 32 bytes.
  • Repeated connection attempts to the device's MQTT broker from unknown IPs.
  • Unusual MQTT topics or payloads containing long strings of repeating characters.

• Host IOCs:

  • Device logs showing stack corruption errors or unexpected reboots.
  • Memory dumps indicating buffer overflow patterns.
  • Presence of shellcode or ROP gadgets in device memory.

• File IOCs:

  • Modified firmware binaries with injected code (if attacker gains persistence).

Detection Engineering

YARA Rule

rule CVE_2024_50694_MQTT_Overflow {
    meta:
        description = "Detects oversized MQTT timestamp fields in network traffic"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-50694"
    strings:
        $mqtt_topic = "sungrow" ascii wide nocase
        $timestamp_key = "\"timestamp\"" ascii wide nocase
        $long_string = /"timestamp"\s*:\s*"[A-Za-z0-9]{33,}"/ ascii wide
    condition:
        $mqtt_topic and $timestamp_key and $long_string
}

Sigma Rule

title: CVE-2024-50694 MQTT Buffer Overflow Detection
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects oversized MQTT timestamp fields indicative of CVE-2024-50694 exploitation
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: mqtt
detection:
    selection:
        payload|contains: "timestamp"
        payload|re: "\"timestamp\"\\s*:\\s*\"[A-Za-z0-9]{33,}\""
    condition: selection
falsepositives:
    - Legitimate long timestamps (unlikely)
level: high

Suricata Rule

alert tcp any any -> any 1883 (msg:"CVE-2024-50694 MQTT Buffer Overflow Attempt"; flow:to_server; content:"timestamp"; content:!"|00|"; pcre:"/\"timestamp\"\s*:\s*\"[A-Za-z0-9]{33,}\"/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Network Segmentation: Place the WiNet-SV200 device on a separate VLAN with strict access controls. Block inbound MQTT traffic from untrusted networks.
2. Disable MQTT: If MQTT functionality is not required, disable it in the device configuration.
3. Monitor Logs: Enable logging and monitor for unusual crashes or reboots.

Long-term Fix:

• Vendor Patch: Await an official firmware update from SunGrow that fixes the buffer overflow. Contact SunGrow support for updates.
• Firmware Hardening: If possible, apply custom firmware or compile with stack canaries and ASLR (if supported by the platform).

Workarounds:

• Use a firewall to restrict MQTT traffic to only trusted IP addresses.
• Implement an MQTT proxy that validates message sizes before forwarding to the device.

Valters IT
DevSecOps & Cyber Threat Intelligence